1. Field of the Invention
The present intention relates to a non-destructive testing system, and particularly relates to a non-destructive testing system that performs non-destructive testing of a joining portion (lamination joining portion) formed by joining lamination of different metal materials or the like.
2. Description of the Related Art
Conventionally, there is known a technology for joining different metal materials in lamination, for example, by resistance spot welding, friction stir welding, or the like.
Patent Document 1 (Japanese Patent Application Laid-Open No. 2009-00700) discloses such a joining method and a joint structure of different metal materials.
Further, as a non-destructive testing method, Patent Document 2 (Translation of PCT Application JP-T-2010-513883) discloses a technology in which a melted portion and a non-melted portion enclosing the melted portion of a material joining portion is heated temporally, for example, in a pulse form of a rectangular wave or in a sine waveform with a certain cycle to obtain thermal images (corresponding to ‘infrared images’ in the present invention) transmitted through the material joining portion, and to detect presence or absence of a melted portion.
Still further, Patent Document 3 (Deutsche Patent Application Laid-Open No. 102008030691A1) discloses a technology for non-destructive testing in which the thickness of foreign matter present inside a testing object is detected by infrared lock-in thermography and a technology for a non-destructive testing apparatus using the technology for non-destructive testing. Patent Document 3 also discloses that the thickness of a foreign matter can be detected as follows. That is, heating is performed in a rectangular waveform or a sine waveform at different frequencies, and pixels of thermal images (corresponding to ‘infrared images’ in the present invention) obtained with the certain cycle are subjected to computation so as to obtain phase images for the respective frequencies. The thickness of a foreign matter can be detected, based on the respective phase images.